1. Field of the Invention
The present invention related generally to a land navigation system, and more particularly to such systems which display, in real time, the position of a vehicle on a map, through an automatic readjustment or correction procedure using digital cartographic data stored in a mass storage unit or mass memory.
2. Description of the Prior Art
The knowledge and real time display, in an autonomous fashion, of the position of a moving land vehicle requires the installation of the following elements in it:
sensors of position, speed and/or acceleration in one or more axes;
a computing device that uses the data given by the sensors to determine the position of the vehicle in terms of geographic coordinates with respect to a universal or local reference system;
a display device to display the position of the vehicle, either by light indication in the form of an alphanumerical or cartographic display, for example by forming a light dot or hair cross on a map (displayed on a display screen on printed or a transparent or paper medium);
an interface circuit between the system and the operator giving the latter, generally the driver of the vehicle, the possibility of initializing the position of the vehicle at the start, and of then actuating the positioning readjustments.
The precision of the localization is directly linked to that of the sensors: this is why the autonomous navigation systems necessitate readjustments to compensate for measurement deviations resulting from imprecision and drifts in the sensors (gyrometers, gyroscopes, odometers, magnetic compasses etc.). These readjustments may be periodic or achieved under certain predetermined conditions. Their frequency is related chiefly to the precision of the sensors, but the choice of high-performance sensors results in high-cost approaches.